UNIVERSITY   OF  CALIFORNIA    PUBLICATIONS. 

COLLEGE  OF  AGRICULTURE. 

AGRICULTURAL  EXPERIMENT  STATION, 

BERKELEY,  CALIFORNIA. 


CALIFORNIA  PEACH  BLIGHT 

By  RALPH  E.  SMITH. 

Assisted  by  E.  H.  Smith,  T.  F.  Hunt,  and  B.  J.  Jones. 


BULLETIN    No.    191. 

UNIVERSITY  OF  CALIFQKJ>OA 

(Berkeley,  Cal.,  September,  1907.)  .   iqq  A  D  V 

COLLEGE  OF  AGRICULTURE 
SACRAMENTO:  DAVB 

W.   W.   SHANNON,      :      :      :      :      SUPERINTENDENT  state   printing. 

1907. 


BENJAMIN  IDE  WHEELER.  Ph.D.,  LL.D.,   President  of  the  University. 


EXPERIMENT  STATION  STAFF. 

E.   J.   WICKSON,   M.A.,    Director  and  Horticulturist. 

E.   W.   HILGARD.   Ph.D..  LL.D.,  Chemist.     • 

W.    A.    SETCHELL.    Ph.D.,   Botanist. 

ELWOOD  MEAD.  M.S.,  C.E..  Irrigation  Engineer. 

C.   W.   WOODWORTH,  M.S.,  Entomologist. 

R.    H.    LOUGHRIDGE,    Ph.D.,    Agricultural    Geologist    and    Soil    Physicist'.       (Soils, 

Alkali.) 
M.  E.  JAFFA,  M.S.,  Nutrition  Expert,  in  charge  of  the  Poultry  Station. 
G.  W.  SHAW.  M.A..  Ph.D.,  Agricultural  Technologist,  in  charge  of  Cereal  Stations. 
GEORGE  E.  COLBY,  M.S.,  Chemist.      (Fruits,  Waters,  Insecticides.) 
RALPH  E.  SMITH,  B.S.,  Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological   Laboratory  and  Experiment   Stations. 
A.   R.   WARD,   B.S.A.,  D.V.M.,   Veterinarian  and  Bacteriologist. 

E.  W.  MAJOR.   B.Agr.,  Animal  Industry  and  Manager  of   University  Farm. 

F.  T.   BIOLETTI,  M.S.,   Viticulturist.      (Grapes,   Wine  and  Zymology.) 
H.   M.   HALL,  M.S.,  Assistant  Botanist. 

H.  J.   QUAYLE,  A.B.,   Assistant  Entomologist. 

W.    T.    CLARKE,    B.S.,    Assistant    Horticulturist    and    Superintendent    of    University 

Extension  in  Agriculture. 
JOHN  S.   BURD,   B.S.,   Chemist,  in  charge  of  Fertilizer  Control. 
C.  M.  HARING,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
E.   B.   BABCOCK,  B.S.,  Assistant  Plant  Pathologist. 
E.  H.  SMITH,  M.S.,  Assistant  Plant  Pathologist. 

J.    W.    MILLS,    Assistant   Horticulturist,     )      CUrus  Experiment  station,  Riverside. 

T.   F.   HUNT,   B.S.,  ) 

H.  J.  RAMSEY,  M.S.,  Assistant  Plant  Pathologist,  I    Southern  California  Pathologi- 

C.    O.    SMITH,    M.S.,  "  "  "  j         cal  Laboratory.     Whittier. 

R.  E.  MANSELL,  Assistant  in  Horticulture,  in  charge  of  Central  Station  Grounds. 

GEO.   W.    LYONS,   B.S.,   Assistant  in  Soil  Laboratory. 

RALPH  BENTON,   B.S.,  Assistant  in  Entomology. 

A.   J.   GAUMNITZ,  M.S.,  Assistant  in  Cereal  Investigations. 

HANS  C.   HOLM,  B.S.,  Assistant  in  Zymology. 

P.   L.  McCREARY,  B.S.,  Laboratory  Assistant  in  Fertilizer  Control. 

C.  WESTERGARD,   B.S.,  Assistant  in  Farm  Mechanics. 

M.   E.   STOVER,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 

D.  L.  BUNNELL,  Clerk  to  the  Director. 


JOHN  TUOHY,  Patron,  \  Tu]SLre  Substation,  Tulare. 

J.   T.   BEARSS,  Foreman,  ) 

J.   W.  ROPER,  Patron,  ) 

E.    C.   MILLER,   In  charge,  $ 


University  Forestry  Station,  Chico. 


ROY  JONES,   Patron,  \          University  Forestry  Station,  Santa  Monica. 

N.   D.   INGHAM,  Foreman,  S                                                                                          f 

VINCENT     J.     HUNTLEY,  Foreman     of     California     Poultry     Experiment     Station, 
Petaluma. 

The  Station  publications  (Reports  and  Bulletins),  so  long  as  avail- 
able, will  be  sent  to  any  citizen  of  the  State  on  application^ 


CALIfORNIA  PEACH  BLIGHT 

By  RALPH  E.  SMITH. 
Assisted  by  E.  H.  Smith,  T.  F.  Hunt,  and  B.  J.  Jones. 


The  disease  which  forms  the  subject  of  this  bulletin  has  come  to  be 
a  well-jknown  factor  in  peach-growing  in  practically  every  part  of 
California  where  the  fruit  is  extensively  grown.  While  its  general 
occurrence  has  been  experienced  only  during  the  past  few  seasons,  the 
disease  has  become  so  abundant  and  its  effects  so  extremely  disas- 
trous that  almost  every  peach-grower  has  come  to  know  it  and  see  the 
necessity  of  finding  some  immediate  preventive  treatment  in  order  to 
save  .his  trees  from  actual  destruction. 

The  present  publication  aims  to  present  the  results  of  three  years' 
experience  and  experimentation  in  the  control  of  this  trouble,  showing 
the  almost  absolute  success  with  which  the  disease  has  been  controlled 
by  treatment.  The  work  has  been  unusually  satisfactory  in  this 
respect,  and  it  has  apparently  been  fully  demonstrated  that  by  proper 
attention  the  grower  can  fully  protect  his  trees  and  crop  from  the 
effects  of  the  blight  at  a  minimum  expense. 

Peach  "blight'  has  been  so  frequently  and  fully  discussed  and 
described  in  our  horticultural  journals  and  meetings  during  the  past 
two  years  that  it  seems  scarcely  necessary  to  consider  in  detail  the 
nature  and  history  of  the  disease  at  this  time.  So  unusually  sudden 
and  pronounced  have  been  the  effects  of  the  trouble  in  practically  all 
the  peach-growing  sections,  and  so  widely  have  methods  of  control 
been  demonstrated  and  urged  upon  the  growers  by  agents  of  the 
Experiment  Station  and  others,  that  we  have  no  plant  disease  in  the 
State  which  is  better  known  or  for  which  control  methods  are  more 
generally  applied  than  this. 

This  disease  appears  to  have  been  present  in  the  State  for  some 
time.  Professor  Pierce  records  it  as  occurring  previous  to  1900,*  and 
some  growers  recognize  the  trouble  as  one  with  which  they  have  been 
familiar  for  a  number  of  years.  It  was  in  the  spring  of  190-4,  how- 
ever, that  the  "blight"  began  to  attract  much  attention.  The  injured 
condition  of  many  trees  at  that  time  was  very  evident.  This  was 
particularly  the  case  in  the  Sacramento,  San  Joaquin,  and  Suisun 
valleys.     A   spotting,    gumming,    and   death   of  the   buds   and   twigs, 

*  Pierce,  Newton  B.  Peach  Leaf  Curl.  Bull.  20,  Div.  Veg.  Phys.  and  Path., 
U.  S.  D.  A.,  1900,  p.  179. 

62354 


71 


UNIVERSITY    OV    CALIFORNIA KXPKHIM10NT    STATION. 


particularly  on  the  lower  part  of  the  trees,  appeared  in  some  abun- 
dance at  that  time.  The  winter  of  1905  was  a  very  wet  one,  and  the 
blight  increased  greatly  that  spring.  By  the  middle  of  February,  1905, 
it  was  evident  in  many  places  that  a  fresh  infection  had  taken  place 
and  the  growers  began  very  generally  to  see  the  necessity  of  finding 
means  of  controlling  this  new  disease.  Since  another  even  more  seri- 
ous orchard  disease,  the  pear  blight,  Avas  making  its  first  appearance 


FIG.  1.     Peach  twigs  affected  by  "blight." 

in  much  of  the  same  territory  at  the  same  time,  the  peach  trouble  was 
considerably  overshadowed  for  the  time.  The  writer  first  became 
familiar  with  the  disease  as  a  serious  matter  in  the  fall  of  1904,  since 
which  time  the  matter  has  been  under  observation  and  experiment  by 
the  Station  to  a  considerable  extent,  culminating  in  the  general  cam- 
paign of  control  in  the  fall  of  1906.  The  blight  was  extremely  preva- 
lent in  the  spring  of  1906,  and  somewhat  less  so,  but  still  very  destruc- 
tive  indeed    in    1907.     Tin-   large   acreage  of  peaches  which  received 


Bulletin    191. 


CALIFORNIA    PEACH    BLIGHT. 


75 


timely  spraying  previous  to  the  latter  season  rendered  the  effects  of 
the  disease  much  less  noticeable.  In  the  unusually  wet  spring  of 
1905,  it  was  noticed  generally  in  the  Sacramento,  San  Joaquin,  and 
other  valleys  that  peach  trees  were  affected  to  an  alarming  extent 
with  some  unusual  condition.     The  trouble  consisted  in  the  dying  of 


FIG.  2.    Peach  orchard,  showing  typical  blight  effect. 

the  buds  on  the  fruiting  wood,  spotting  of  the  green  twigs,  and  drop- 
ping or  non-development  of  the  young  leaves  and  fruit.  Particularly 
noticeable,  and  the  most  prominent  feature  of  the  disease,  was  a  copi- 
ous "gumming,"  or  exudation  of  masses  of  gelatinous  sap  from  the 
twigs,  originating  in  the  dead  spots  and  buds.  This  gumming  was 
extremely  abundant  in  wet  weather  all  over  the  one-year-old  fruiting 
twigs  of  affected  trees,  and  with  the  blighted  leaves  and  fruit  and 


(6 


UNIVERSITY  OF   CALIFORNIA — EXPERIMENT   STATION. 


spotted,  leafless,  dead  or  dying  twigs  and  shoots,  gave  the  tree  a  most 
distressing  and  alarming  appearance.  The  crop  was  entirely  ruined 
in  badly  affected  orchards  and  the  trees  brought  into  an  extremely 
weakened  condition.     (Figs.  1  and  2.) 

This  describes,  in  a  general  way,  the  nature  of  this  disease.  It  is 
readily  distinguished  from  any  other  peach  trouble  by  the  features 
mentioned.  It  is  essentially  a  winter  or  early  spring  disease  of  the 
fruiting  twigs,  the  one-year-old  wood  which  is-  the  valuable  part  of  the 


FIG.  3.    Effect  of  blight  on  fruit  of  peach. 


tree.  This  growth  becomes  killed  all  through  the  tree,  except  in  the 
very  top,  and  very  serious  loss  and  injury  result.  Most  of  the 
infection  takes  place  in  the  winter,  before  the  new  growth  starts,  on 
twigs  which  were  healthy  and  free  from  the  trouble  at  the  end  of  the 
ing  season  the  previous  fall.  The  new  fruit  becomes  affected  to 
some  extent,  as  shown  in  Fig.  3,  but  the  principal  damage  is  done  by 
the  killing  of  the  buds  and  whole  twigs  at  a  period  previous  to  the 
deyelopment  of  fruit. 

During  1905  and  1906  the  disease  occurred  in  greater  abundance. 
appearing  in  all  the  peach-growing  sections.  Santa  Clara  County  and 
the  southern  California  peach  sections  were  the  last  affected,  but  the 


Bulletin  191. 


CALIFORNIA   PEACH   BLIGHT. 


77 


blight  now  occurs  in  both  regions.    The  losses  occasioned  by  the  '  *  blight ' ' 
have  been  enormous,  particularly  in  the  seasons  above  mentioned  when 


FIG.  4.    Peach  tree  sprayed  in  December,  1905.    Photo  taken  in  May,  1906.    Compare  with  Fig.  2. 

climatic  conditions  were  particularly  favorable  and  little  was  done  to 
check  the  disease.  Indeed,  it  may  truthfully  be  said  that  in  the  sum- 
mer of  1906,  after  two  years  of  active  prevalence  of  the  "blight,"  the 


f«  UNIVERSITY    OV   CALIFORNIA — EXPERIMENT   STATION. 

peach  orchards  of  the  Sacramento  and  San  Joaquin  valleys,  the  main 
commercial  acreage  of  the  State,  would  have  been  in  an  absolutely 
ruined  and  unproductive  condition  without  some  means  of  checking  the 
disease.  The  trouble  was  abundant  in  every  orchard,  all  varieties  were 
more  or  less  affected,  and  the  younger  growth,  which  in  the  peach  bears 
the  fruit,  had  been  almost  completely  killed  and  further  development 


FIG.  5.    Effects  of  blight. 

prevented.     With   the   disease   unchecked  peach-growing   was   appar- 
ently at  an  end. 

THE  CONTROL  OF  THE  BLIGHT. 

Most  fortunately,  under  these  serious  conditions,  there  has  been 
evidence  almost  from  the  first  that  the  disease  could  be  successfully 
controlled.  When,  in  1904  and  1905,  the  blight  began  to  be  abundant 
enough  to  attract  notice,  it  was  evident  to  all  who  observed  the  matter 
closely  that  the  usual  practice  of  peach  spraying  in  February  or 
March  was  too  late  to  check  infection  by  this  disease.  Twigs  which 
were  sound  and  healthy  in  December  were  found  to  be  spotted  with 
infection  \>y  the  first  of  February.     Evon  with  the  heaviest  and  most 


Bulletin  191. 


CALIFORNIA   PEACH   BLIGHT. 


79 


thorough  spraying  with  Bordeaux  mixture,  or  lime,  salt  and  sulfur, 
applied  at  the  usual  time,  the  gumming  produced  by  the  blight  would 
be  found  breaking  out  directly  through  the  spray  coating  on  affected 
twigs,  and  the  disease  was  not  checked  in  the  least  by  the  application. 
Knowing  the  cause  of  the  disease  to  be  a  parasitic  fungus,  and  with 
this  habit  of  midwinter  infection  and  development  suggested  by  the 


FIG.  6.    Results  of  December  spraying.    Compare  with  Fig.  5. 

experience  of  1904  and  1905,  the  idea  became  quite  general  by  the  fall 
of  1905  that  spraying  in  December  would  be  the  most  promising  time 
for  successful  control.  The  disease  being  new,  and  the  fall  season  of 
1905  an  exceptionally  dry  one,  the  majority  of  the  growers  held  to 
the  hope  that  the  blight  would  not  occur  again  as  before  and  took  no 
unusual  means  for  its  control.  Several  in  the  Suisun  Valley,  however, 
and  a  few  in  the  San  Joaquin  and  elsewhere,  sprayed  their  trees  in 
December,  and  when  the  very  severe  development  of  the  disease  came 
on  in  February,  1906,  the  results  were  most  complete  and  striking, 
showing  in  general  that  one  thorough  spraying  early  in  December 
with  the  Bordeaux  mixture  absolutely  prevented  the  disease.     (Fig.  4.) 


sM  UNIVERSITY    OF   CALIFORNIA EXPERIMENT    STATION. 

After  December  results  were  not  so  good,  and  gradually  deteriorated 
up  to  February,  from  which  time  on  sprayed  trees  were  no  better  than 


FIG.  7.     Effects  of  blight  on  fruiting  twigs,  1906. 

onsprayed  in  respect  to  this  disease.  One  orchard,  sprayed  mostly  in 
December,  but  finished  out  Late  in  January,  showed  a  decided  differ- 
ence  in  the  two  portions.     Spraying  in  December  was  perfectly  sue- 


Bulletin  191. 


CALIFORNIA   PEACH  BLIGHT. 


81 


cessful;  in  January  partially  so,  and  in  February  and  March  without 
effect  on  this  disease.     The  blight  was  so  bad  in  unsprayed  or  late- 


FIG.  8.    Twigs  from  December-sprayed  tree,  1906. 

sprayed  orchards,  with  the  crop  and  foliage  almost  entirely  gone,  and 
all  the  growth  on  those  sprayed  in  December  perfect,  particularly  the 
lower,   inner,   blight-susceptible   fruiting  twigs,   that   one  seldom   sees 


—  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

so  striking  a  contrast  in  the  treatment  of  any  plant  disease.  Abundant 
comparison  was  available  between  trees  of  the  same  variety,  age,  and 
condition.      (Figs.   5  and  6.) 

Effect  on  Curl  Leaf  Equally  Good.— The  writer  took  some  pains 
to  note  in  this  connection  the  effect  of  this  early  spraying  on  curl  leaf, 
inasmuch  as  any  peach  treatment  must  take  this  disease  into  consid- 
eration. (Fig.  7.)  So  far  as  could  be  judged,  the  effects  were  equally 
good,  and  the  disease  controlled  as  well  as  by  the  usual  later  spraying. 
The  fine  condition  of  a  block  of  December-sprayed  Susquehannas  was 
especially  noticed,  while  uhsprayed  trees  on  this  and  even  less  curl- 
susceptible  varieties  were  badly  affected  by  c,url  leaf  wherever  the 
blight  fungus  had  left  any  leaves  on  the  tree.     (Fig.  8.) 

To  summarize:  Unsprayed  trees  were  very  badly  affected  by  blight 
and  curl  leaf. 

Trees  sprayed  in  December  were  free  from  any  disease. 

Trees  sprayed  late  in  January  were  somewhat  affected  by  blight, 
but  free  from  curl  leaf. 

Trees  sprayed  in  February  and  early  March  were  free  from  curl, 
but  no  better  than  the  unsprayed  in  regard  to  blight. 

In  the  light  of  these  results  and  in  view  of  the  serious  and  demoral- 
ized condition  of  the  peach  industry  in  the  spring  of  1906,  a  thorough 
campaign  of  peach-spraying  and  experimentation  was  planned  by  the 
Station  for  the  season  of  1906-07.  So  bad  was  the  condition  of  prac- 
tically every  orchard  that  it  was  not  deemed  sufficient  to  simply  carry 
out  a  few  limited  demonstrations  and  experiments.  In  order  to  meet 
the  situation  adequately  it  was  necessary  that  practically  every  grower 
in  the  principal  sections  be  personally  visited  and  instructed  in  the 
best  method  of  procedure,  in  order  that  no  further  time  be  lost.  In 
accordance  with  this  plan  assignments  were  made  to  Messrs.  Jones 
and  Hunt  to  the  Sacramento  and  San  Joaquin  valleys,  respectively,  to 
urge  the  growers  to  spray  in  November  and  December,  to  instruct  and 
assist  the  inexperienced  in  proper  methods  of  work,  and  to  follow  up 
the  work  done  and  the  results  accomplished.  Series  of  experiments  were 
also  carried  out,  in  spraying  at  different  seasons,  for  blight  control. 
In  addition  to  the  Station  efforts,  great  good  was  accomplished  by  the 
Boards  of  Horticulture  in  many  of  the  counties  along  the  same  line. 
Early  spraying  was  urged  upon  the  growers  at  every  opportunity  by 
these  men  in  the  valley  counties  and  elsewhere,  and  many  a  1907  crop 
is  the  result  of  their  efforts.  The  State  Commissioner  of  Horticulture 
was  a] so  active  in  spreading  the  propaganda. 

As  a  result  of  this  effort  and  the  very  serious  condition  of  the  peach 
orchards,  spraying  in   November  and  December,  1906,  was  almost  uni- 


Bulletin  191.  CALIFORNIA  PEACH  BLIGHT.  83 

versal  in  the  San  Joaquin  and  Sacramento  valleys.  Such  a  concerted 
and  general  effort  has  rarely  been  made  in  the  attempt  to  control  any 
plant  disease.  From  October  to  March  the  Experiment  Station  repre- 
sentatives were  constantly  in  the  field  in  the  upper  San  Joaquin  and 
lower  Sacramento,  our  greatest  peach  sections.  The  recommendation 
made  was'  to  spray  between  November  15  and  December  15,  with 
Bordeaux  mixture  of  the  strength  30-35-200  (Milestone,  lime,  water). 
The  work  was  entirely  new  to  many  of  the  growers,  particularly  in  the 
San  Joaquin  Valley,  where  there  had  been  little  cause  for  spraying 
peaches  hitherto,  and  much  time  was  spent  in  instructing  the  inex- 
perienced in  making  the  mixture  and  applying  it  to  the  trees.  The 
fact  that  four  hundred  spray  pumps  were  sold  at  one  small  town,  as 
recorded  by  a  horticultural  paper,  indicates  both  the  extent  of  the 
operations  and  the  fact  that  it  was  new  to  most  of  the  growers.  Natu- 
rally, under  these  circumstances,  many  mistakes  were  made  and  much 
poor  spraying  resulted.  Another  season  will  certainly  find  the  grow- 
ers much  better  prepared  to  spray  their  trees  properly.  Weather  con- 
ditions also  were  most  unfavorable  to  spraying  at  the  desired  time,  on 
account  of  continuous  rain.  The  condition  of  the  trees  resulting  from 
previous  attacks  of  the  disease  was  also  to  be  considered.  To  one 
familiar  with  the  state  of  a  large  part  of  our  peach  orchards  in  the 
spring  of  1906  it  would  seem  little  short  of  miraculous  to  have  any- 
thing like  a  full  crop  in  1907  on  the  same  trees,  and  in  fact  even  less 
surprising  if  the  trees  had  all  died.  With  all  the  lower  twig  growth 
killed,  most  of  the  leaves  fallen  in  early  summer,  the  crop  almost 
entirely  on  the  ground,  no  wood  developing  for  a  new  crop,  and  the 
whole  life  of  the  tree  confined  to  a  few  straggling  twigs  in  the  top,  the 
outlook  at  the  end  of  last  season  was  indeed  discouraging. 

Still  further  trouble  was  caused  by  a  shortage  of  bluestone,  many 
being  totally  unable  to  procure  the  material,  and,  if  at  all,  only  at  an 
exorbitant  price.  All  in  all,  therefore,  the  results  of  the  past  season 
may  be  taken  as  a  very  conservative  basis  for  future  calculations. 

The  time  suggested  for  spraying  was  chosen,  as  already  shown,  on  the 
basis  of  the  limited  experience  of  the  previous  season  and  the  known 
fact  of  the  time  of  infection.  After  following  the  matter  carefully 
for  several  seasons  it  has  appeared  that  each  year  about  the  first  week 
in  January  the  signs  of  the  disease  make  their  appearance.  At  this 
time  the  indications  of  the  blight  of  the  previous  year  are  very  abun- 
dant everywhere  in  the  shape  of  dead,  cankered  spots  on  the  growth  of 
the  preceding  year.  From  these  spots  copious  gumming  begins  with 
the  winter  rains.  Up  through  December,  however,  the  new  growth  of 
th^  season,  the  young  twigs  which  bear  the  fruit  buds,  are  green  and 
vigorous,  save  for  a  very  few  occasional  blight  spots  which  may  have 
formed  early  in  the  preceding  summer.     The  buds  are  alive  and  vigor- 


84 


UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 


ous,  and  on  what  bearing  wood  there  is  the  indications  are  in  no  way 
other  than  tor  a  good  crop.     In  the  ease  of  very  heavy  rains  previous 

to  the  first  of  Jan- 
uary there  may  be 
considerable  infec- 
tion even  before 
that  date,  as  oc- 
curred in  Decem- 
ber to  some  extent 
during  the  past 
season,  but  the 
main  infection  ap- 
pears to  come  on 
quite  uniformly  at 
about  the  time  of 
the  new  year. 
From  this  time  on 
through  the  winter 
further  infection 
is  abundant  and 
rapid,  occurring  in 
proportion  to  and 
along  with  the 
rainfall.  Up  to 
December  15th  al- 
most every  twig  is 
green,  sound,  and 
unaffected.  With 
abundant  rain  be- 
fore or  about  that 
time  the  brown,  or 
at  first  reddish, 
dead  spots  begin  to 
appear,  especially  at  the  base  of  the  buds  just  where  they  join  the  twig. 
(Fig.  7.)  In  this  way  the  buds  are  killed  and  the  crop  as  well  as  the 
growth  for  the  next  year  is  destroyed.  This  has  not,  in  our  observations, 
become  abundant  until  January  1st,  about  which  time  the  infection 
occurs  very  rapidly.  In  this  way  twigs  which  were  entirely  sound  late 
in  December  may  have  almost  all  their  buds  and  the  twig  itself  killed, 
spotted,  and  gumming  six  weeks  later. 

The  results  of  spraying  in  the  fall  of  1906  became  very  apparent  by 
February  1st.  Trees  well  sprayed  before  the  infection  started  had  the 
twigs  and  burls  still  alive  and  sound,  while  unsprayed  trees  were  show- 


FIG.  9.    Unsprayed  trees,  190' 


Bulletin  191. 


CALIFORNIA    PEACH    BLIGHT. 


85 


ing  very  bad  infection  and  gumming.  In  one  case  the  writer  saw  an 
orchard  on  January  8th  which  was  just  then  being  sprayed,  and  in 
which  the  work  was  stopped  before  completion,  on  account  of  rain. 
On  the  last  rows  sprayed,  as  well  as  on  those  unsprayed,  the  blight 
spots  were  appearing  in  great  abundance  on  the  twigs,  breaking  out 
directly  through  the  spray  in  numerous  cases,  and  it  was  most  evident 
that  so  far  as  blight  was  concerned  the  best  time  for  treatment  had 
passed,  though  spraying  might  still  prevent  further  infection,  which 
might  result  from  more  rain. 

A  very  important  complication  must  be  considered  in  spraying  for 
blight  control;  this  is  the  occurrence  of  another  peach  disease,  the 
Curl  Leaf.  The 
effects  of  this 
trouble  are  too  well 
known  in  Califor- 
nia to  need  descrip- 
tion. The  control 
of  the  disease  is 
very  successfully 
accomplished  by 
spraying  in  Feb- 
ruary or  March, 
just  before  the 
buds  unfold,  but 
a  time  which,  as 
has  already  been 
shown,  is  too  late 
for .  blight  preven- 
tion. In  the  expe- 
rience of  1905  the 
one  fall  spraying 
controlled  both  dis- 
eases— a  most  satis- 
factory condition. 
In  the  spring  of 
1907,  however,  a 
very  virulent  at- 
tack of  curl  leaf 
occurred,  especially 
in  the  lower  Sacra- 
mento Valley,  while 
the  blight  fungus  proved  somewhat  less  active  than  in  the  previous 
season.     The  result  of  this  is  plainly  shown  by  the  results  of  spraying, 


FIG.  10.    Tree  sprayed  in  November,  1906,  and  February,  1907. 


•M 


UNIVERSITY    OV   CALIFORNIA — EXI'KKl.MKNT    STATION. 


viz:  that  the  November  or  December  application  did  not  entirely  hold 
the  curl  Leaf  in  cheek,  although  as  successful  as  before  with  the  blight. 

Consequently   some   orchards    sprayed   properly    and   successfully   for 

blight  were  badly 
injured  by  curl 
leaf,  while  others 
sprayed  later  were 
protected  from  curl 
leaf  and  left  in 
better  condition  at 
the  end  of  the  sea- 
son than  those  in 
which  the  blight 
alone  was  con- 
trolled. All  that 
had  been  expected 
of  the  blight  treat- 
ment held  good 
when  its  effects 
wrere  differentiated 
from  those  of  the 
other  disease,  but 
the  necessity  of  two 
sprayings  rather 
than  one  for  the 
positive  control  of 
both  diseases  has 
become  evident. 

The  following 
table  gives  in  con- 
densed form  the 
record  of  a  number 
of  typical  orchards 
in       the       regions 


FIG.  11. 


Left  side  of  tree  sprayed  in  December,  1906, 
right  side  unsprayed. 


where  our  work  was  centered.  The  column  of  formulas  expresses  the 
amount  of  bluestone,  lime,  and  water  used  in  each  instance.  The  names 
of  varieties  are  abbreviated  as  follows:  .C,  Crawford;  CI,  Crawford 
Late;  E,  Elberta;  F,  Foster;  G,  Georgia;  Ha,  Hale;  H,  Henrietta; 
I,  Imperial;  L,  Lovell;  Mc,  McDevitt;  Ma,  Mary's  Choice;  Mu,  Muir; 
0,  Orange;  P,  Phillips;  Sa,  Salway;  Su,  Susquehanna;  T,  Tuscan; 
W.  Wheatland. 

In   orchard   No.    1,   for  instance,  Muirs,  Lovells,  and  Elbertas  were 
sprayed    December  22d   and  in   February,   each  time  with  Bordeaux 


Bulletin  191. 


CALIFORNIA   PEACH   BLIGHT. 


87 


mixture  made  with  30  pounds  of  bluestone,  30  pounds  of  lime,  and  200 
gallons  of  water. 

The  acreage  represented  in  this  table  is  about  2,500.     The  orchards 
sprayed  in  the  fall  of  1906  for  blight  control,  as  a  result  of  the  efforts 


FIG.  12.    Twigs  from  sprayed  and  unsprayed  trees,  1907. 

of  the  Experiment  Station  and  others,  amounted  certainly  to  ten  times 
this  amount,  or  25,000  acres  at  a  very  conservative  estimate,  as  there 
are  at  least  50,000  acres  of  bearing  peaches  in  the  area  under  observa- 
tion and  an  unsprayed  orchard  was  very  much  the  exception.  The 
data  given  in  the  table  are  representative  of  average  conditions,  taking 


UNIVERSITY   OF  CALIFORNIA — EXPERIMENT   STATION. 

the  orchards  as  they  come,  from  which  it  appears  that  most  of  the 
orchards  were  sprayed,  and  a  very  large  majority  at  the  proper  time 
and  with  good  results. 

Cases  like  Nos.  89  and  124  show  the  loss  of  practically  the  whole  crop 
where  no  spraying  was  done,  and  Figs.  9,  10,  11  and  12  indicate 
plainly  the  comparative  results  of  proper  spraying  and  no  treatment. 
Fig.  11  is  particularly  suggestive,  showing  on  the  same  tree  a  heavy 
crop  and  full  foliage  on  one  side,  which  was  sprayed,  and  the  complete 
blighting  and  ruining  of  the  crop  on  the  other  side,  which  received  no 
treatment.  In  view  of  these  results  a  saving  of  $20  per  acre  is  cer- 
tainly a  moderate  estimate,  which  on  the  acreage  stated  would  amount 
to  a  gain  of  $500,000  in  the  season's  crop,  not  considering  the  saving 
of  the  trees  and  possibilities  of  even  better  results  in  the  future.  As  a 
matter  of  fact  the  saving  effected  might  reasonably  be  estimated  as  the 
difference  between  no  crop  at  all  and  a  large  and  profitable  one,  as  well 
as  the  saving  of  the  trees  themselves,  in  which  case  the  figures  would 
rise  very  much  higher.  As  the  whole  expense  to  the  State  and  counties 
for  this  saving  was  probably  not  over  $1,500,  the  practical  value  of 
this  work  is  quite  apparent. 

RECORD  OF  TYPICAL  PEACH  SPRAYING,   1906-07. 


No.        Locality.  Varieties 


Bordeaux 
Formula.  uaies. 


Results  and  Remarks. 


1    Hanford.- 

2 

3 

4 

5  " 

6 

7 

9 


10 


11 
12 
13 
li 
i.-, 
16 
17 


Mu,  L,  E 
Mu 


Mu,  E,  T,  P, 

H,Mc 
Mu,    L,    Su, 

Sa,  P,  O 
Mu,  E 


Young  trees 

F,  Mu,L,  E, 

O 
E,  P,  W,  Mu 

Mu,  C,  S  .-.. 

Mu,  E,  P.... 

Mu  — 

Mu.  E,  T,  L 

Mu,  E 

Mu,E,Cl,Sa 

Mu,  CI,  Su, 
E 

Very  old 
tre<-s 


30-30-200 

30-35-200 

24-40-200 

30-36-200 

30-40-200 

30-35-200 

30-35-200 
20-20-200 
30-30-200 

30-35-200 
20-25-200 
30-40-200 

32-32-200 

40-48-200 

16-20-200 

32-36-200 

30-35-200 

30-35-200 
20-20-200 


Dec.  22,  '06 
Feb.  '07 

Dec.     5,    '06 

Nov.  15,    '06 

Dec.   26,   '06 

Dec.  5-30,  '06 

Dec.  '06 

Dec.  8-30,  '06 
Feb.  '07 

Dec.  1-20,  '06 
Feb.  '07 

Dec.  7,  '06 
Jan.  2,  '07 
Dec.  1-30,  '06 

Dec.  12-22/06 

Nov.29-Dec. 

10, '06 
Dec.  8-15, '06 
Feb.  '07 

Dec.  15-18, '06 

Nov.  20,  '06 

Jan.  5,  '07 

Dec.  '06 

Feb.  '07 


Trees  in  fine  shape.    Big  crop. 

No  blight. 
Big  crop.     No  blight. 

Little  or  no  blight.     Fine  crop. 

Little  blight  on  old  trees.   Some 

curl  leaf.     Fine  crop. 
Old  trees  ;  considerable  blight 

Poor  spraying  in  part. 
Trees   in    tine    condition.     No 

blight. 
Very  little  blight.    Good  crop. 

Trees  look  tine. 
Good  crop.    Very  little  blight. 

Poor  job  first  spraying;  second 
good.     Big  crop.     Trees  tine. 

Very  little  blight.  Trees  look 
well. 

No  blight.     Trees  fine. 

Young  trees.     No  blight. 
No  blight. 

Little  blight  in  very  old  trees ; 

others  good. 
Poor  work  at  first,  but  repeated. 

No  blight.  Best  crop  ever  had. 
Trees  fine.     Very  little  blight. 

Heavv  crop.      Very    bad   in 

1905-6. 


Bulletin  191. 


CALIFORNIA   PEACH  BLIGHT. 


89 


RECORD  OF  TYPICAL  PEACH  SPRAYING,   1906-07 -Continued. 


No. 

Locality. 

Varieties. 

Bordeaux 
Formula. 

Dates. 

Results  and  Remarks. 

32 

Dinuba  ... 

Mu,L 

40-48-200 

Dec.    17,    '06 

Poor  spraying.     Trees  and  crop 
poor.     Some    blight;     much 

curl  leaf. 

33 

" 

Mu,  E,  I,  P, 

O 

40-48-200 

Dec.    13,    '06 

Elbertas    curled    badly.     Very 

poor  spraying.    Some  blight. 

Very  little  blight.     Good  crop. 

34 

" 

Various 

24-24-200 

Dec.     8,    '06 

Feb.   22,   '07 

35 

" 

Mu,  C,  E.__ 

25-25-200 

Dec.  19-30, '06 

Little    blight.     Some    curl    on 
Elbertas. 

36 

u 

Mu,  L,  P.... 

36-36-200 

Dec.   24,    '06 
Feb.   15,   '07 

Little  or  no  blight.     Good  crop. 

37 

" 

Mu,  L 

36-36-200 

Dec.    12,    '06 
Feb.    15,    '07 

No  blight.     Good  crop. 

38 

" 

Mu,  L,  P,0, 
T,  E,  W 

28-32-200 

Dec.     1,    '06 
Feb.    15,   '07 

No  blight.     Good  crop. 

45 

Armona  _. 

Mu,  E,  L.__. 

28-40-200 

Dec.   22,    '06 

No  blight. 

46 

" 

Mu,  E,  L.._. 

28-40-200 

Dec.   29,   '06 

No  blight.     A  little  curl  leaf. 

47 

« 

Su,  Sa,  CI... 

28-40-200 

Dec.   20,    '06 

Little  or  no  blight. 

48 

" 

Mu,  L,  E.._. 

30-44-200 

Dec.   29,    '06 

No  blight. 

49 

" 

Mu,  E.  C,  O, 

Su 

24-28-200 

Dec.  5-24,  '06 

A  little  blight  and  much  curl 
leaf. 

50 

" 

Mu,C,0,Sa, 
Su,  CI 

24-40-200 

Dec.  10-19, '06 

No  blight. 

56 

Kingsburg 

O,    Mu,   Sa, 
F,  Su 

40-48-200 

Dec.   16.   '06 

No  blight.  Big  crop.  A  few 
trees  not  sprayed  have  no 
crop  and  bad  blight. 

Very  little  blight     Good  crop. 

57 

" 

Mu,  O,  T,  C, 

Su 
Mu,  0,  P.... 

48-48-200 

Dec.   15,    '06 

58 

" 

36-40-200 

Nov.  20,    '06 

No  blight.    Heavy  crop. 

59 

« 

T,  P,  0,Mu, 

L,Su 
Mu,  O,  E,  F. 

36-40-200 

Dec.   12,    '06 

No  blight.     Fine  crop. 

60 

" 

40-48-200 

Dec.    15,    '06 

No  blight.     Fine  crop. 

61 

C( 

C,  L,  O 

36-40-200 

Dec.   18,    '06 

Did   poor  iob.      Much   blight. 

Verv  light  crop. 

72 

Del  Key... 

Mu,C,0,Sa, 

30-35-200    Dec.   17,    '06  !  Very  'little  blight.     Fine  crop. 

Su,  P 

20-20-200    Feb.   15,    '07  1 

73 

Visalia 

P 

40-48-200 

Dec.     1,    '06    One  row  poorly  sprayed,  badly 

blighted.     On    the    rest    no 
blight. 
Trees  badly  injured  by  standing- 
water. 

74 

(< 

P,0 

40-48-200 

Nov.  27,    '06 

75 

" 

Ma,  Mu,  O, 

E,  C,Sa,  P 

Mu,  Su,  O... 

48-48-200 

Dec.    12,    '06 

Very  poor  work.     Much  blight. 

84 

Selma 

40-48-200 

Sept.    1,    '06 

Poor    spraying.     Considerable 

Jan.           '07 

blight  and  light  crop. 

85 

" 

P,  0,  Mc__„ 

32-42-200 

Dec.    14,    '06 

No   blight;    a  little  curl   leaf. 

20-20-200 

Feb.           '07        Fine  crop. 

86 

ii 

Mu,  C,  O.... 

30-35-200 

Dec.   20,    '06    Poor  job.     Much  blight.     Fair 

89 

Sultana... 

Unknown. ... 

Not  spra 

crop, 
yed..   Trees     badly    blighted.     Very 

little  fruit. 

109 

Yuba  City. 

T,  Mc,  0,  F, 

20-20-200 

Sept.  25,  '06 

Badly  affected  with  blight  and 

Mu, 

curl  leaf. 

109  A 

24-24-200 

Sept.  25,  '06 

Showed  some  advantage  over 
last  in  blight,  but  bad  with 
curl  leaf. 

109  B 

" 

" 

20-20-200 

Sept.  25,  '06 
Feb.    13,  '07 

Much    better  than   last,    espe- 
cially in  regard  to  curl  leaf. 

109  C 

w' 

(< 

20-20-200 

Oct.    24,   '06 

Little  blight,  but  bad  with  curl 

leaf. 
Somewhat  better  than  last  re- 

109 D 

K 

« 

30-35-200 

Oct.     24,  '06 

garding  blight. 

90 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT   STATION. 


RECORD  OF  TYPICAL  PEACH  SPRAYING,   1906  07— Continued. 


No. 


110 
110  A 
110  B 

111 
1112 

112  A 
113 

113  A 

114 

114  A 
115 

115  A 
115  B 
116 
117 
118 
119 
120 
121 
122 
122  A 
123 
124 
124  A 
125 
142 

12*; 

127 
127  A 


Loealitv 


Varieties 


Yuba  Citv    T.  Me,  O,  F. 
Mu 
T,  Mc 


Bordeaux 
Formula. 


Dates. 


P.  Me.... 
P,  Mc... 
Unknown  .. 
Mu,  I,  Ha  .. 


T,Mc,0,W, 

Mu 
C  . 


Marysville 

Chico 


Red  Bluff 
Oakdale  .. 


Unknown  .. 
Unknown  .. 
Mu,  0,T.__. 

P 

P 

C,  Su,  G  .... 

Apricot 

Unknown 
Unknown 
Unknown 
Unknown 
Unknown 
Unknown 
Various... 

F 

Mu 

Bidwell... 
Various.. . 


20-20-200 
30-35-200 
30-35-200 
30-35-200 
30-35-200 
30-35-200 

30-35-200 
30-35-200 
30-35-200 
30-35-200 
Not  spra 
36-40-200 
36-40-200 
36-40-200 


Mu.   C,  Ma, 

CI 
Cling 


30-35-200 
40-60-200 
.    40-60-200 


60-72-200 
36-36-200 
30-35-200 
36-36-200 
30-35-200 
Unknown 
Unknown 

Rex 

Unspray 
Unspray 
Unspray 
Unknown 


!  Feb.  13,    '07 

Dec.  1,    '06 

Jan.  '07 

Feb.  '07 

Feb.  15,    '07 

Nov.  27  to 

Dec.  20,  '06 
Mar.     6,    '07 

Nov.  20,    '06 

Nov.  20,    '06 

Nov.  20,  '06 
Mar.  1,  '07 
Mar.  13,    '07 

yed 

Feb.   10,    '07 

Jan.    18,    '07 

Jan.    18,  '07 

Feb.   10,  '07 

Nov.  '06 

Feb.   10,  '07 

Nov.     7,  '06 


Results  and  Remarks. 


Dec.      7, 

Feb.     5, 

Feb. 

Nov.  10, 

Nov. 

Feb. 

Feb. 

ed 

ed 

ed 


'(it; 
'07 
'07 
'06 
'06 
;07 
'07 


Nov.   '06,   to 
Mar.  '07. 

Jan.    10,    '07 

Dec.     7,    '06 

Dec.    14,    '06 


Considerable  blight.  Good 
control  of  curl  leaf. 

Very  free  from  blight;  con- 
siderable curl  leaf. 

More  blight  than  last.  Less 
fruit.     Less  curl. 

Very  bad  with  blight.  Free 
frbm  curl. 

Blight  very  bad.  Good  con- 
trol of  curl  leaf. 

Very  little  blight,  or  curl  leaf. 


Even  less  blight  infection  than 

last. 
Very  little  blight;  considerable 

curl  leaf. 
Free  from  blight  and  curl  leaf. 

Blight    very    bad;    very   little 

curl  leaf. 
Blight  and  curl  leaf  very  bad. 

Some  blight,  but  fairly  good. 

Quite  bad  with  blight  and  curl 

leaf. 
Less  curl  leaf  than  last. 

Fine  condition.     No  blight  or 

curl  leaf. 
Crop  spoiled  by  rain,  but  full 

bloom  and  foiiage. 
No' blight. 

Blight  very  bad. 

Blight  very  bad. 

Very  little  blight. 

Very  little  blight. 

Part  of  same  orchard  as  last. 

Blight  much  worse. 
Twigs  already  infected.    Blight 

abundant. 
Blight  and  curl  very  bad.    No 

crop. 
Blight    less    than    last.      Curl 

very  bad.     Light  crop. 
Blight  and  curl  very  bad. 

Excellent  blight  and  curl  leaf 
control  by  fall  and  spring 
spray. 

Considerable  previous  blight 
infection.    Checked  bv spray. 

No  blight. 

Part  of  same  orchard  as  last. 
Rain  Dec.  10.  Some  infec- 
tion on  these. 


The  records  in  this  table  represent  sprayings  with  various  strengths 

of  Bordeaux  mixture,  in  a  number  of  sections  of  the  Sacramento  and 

Joaquin  valleys,  at  limes  ranging  from  September  to  March,  and 


Bulletin  191.  CALIFORNIA  PEACH  BLIGHT.  91 

on  all  the  usual  varieties  of  peach.     A  study  of  this  table  gives  a  clear 
idea  as  to  the  most  successful  manner  of  treatment. 

Time  of  Spraying  for  Blight  Control.  —  September  was  too  early 
and  February  and  March  too  late.  Spraying  in  the  latter  part  of 
October  seemed  effective,  and  from  then  on  to  the  middle  or  last  of 
December  the  best  results  of  one  application  were  secured  in  preventing 
blight  infection. 

The  attacks  of  curl  leaf  complicated  matters.  In  many  cases  a  com- 
plete blight  control,  obtained  by  early  spraying,  was  nullified  by 
unchecked  attacks  of  the  other  disease.  Spraying  in  November  and 
December  did  not  altogether  hold  the  curl  in  check,  while  the  February 
and  March  applications  did  so  perfectly.  It  therefore  seems  best  in 
the  future  to  advise  two  sprayings,  one  early  and  one  late,  to  insure 
freedom  from  both  diseases. 

As  a  third  peach  pest,  the  Peach  Worm  may  be  controlled  by  spray- 
ing with  lime,  salt,  and  sulfur  just  before  the  buds  open,  a  treatment 
that  is  equally  efficacious  for  curl  leaf,  we  suggest  this  for  the  second 
spraying  rather  than  Bordeaux  mixture.* 

Kind  of  Mixture.— Practically  all  these  results  refer  to  Bordeaux 
mixture.  We  have  reason  to  feel  sure  that  lime,  salt,  and  sulfur  spray 
would  give  equally  as  good  results,  but  for  the  blight  alone  the  more 
easily  prepared  Bordeaux  is  usually  preferable. 

Proportion  of  Mixture. — We  have  not  laid  great  stress  on  the  exact 
formula  for  the  Bordeaux  mixture  to  be  used.  Where  the  mixture  was 
properly  prepared  very  little  difference  in  the  results  has  appeared, 
whether  it  was  20-20-200,  30-35-200,  or  very  much  stronger  as  some 
have  used  it.  Ordinarily  the  20-20-200  formula  is  probably  strong 
enough  and  affords  some  saving  of  material  over  a  heavier  application. 
A  mixture  containing  more  copper  and  lime  remains  longer  on  the 
tree,  however,  is  not  as  quickly  washed  off  by  rain,  and  shows  more 
plainly  on  the  tree  just  how  thoroughly  it  has  been  covered.  We 
would  therefore  advise  the  use  of  the  lesser  strength  only  when  mate- 
rials are  very  high  and  scarce  or  where  the  workmen  are  particularly 
adept  in  applying  the  spray  perfectly.  For  average  conditions  we  pre- 
fer the  30-35-200  for  the  early  application. 

Preparing  the  Mixture.— The  preparation  of  Bordeaux  mixture  has 
been  described  almost  too  frequently  to  need  repetition.  The  lime 
should  be  of  the  best  and  perfectly  unslaked,  and  slaked  in  a  consider- 
able amount  of  the  water  and  stirred  and  strained  to  make  a  perfectly 
smooth  whitewash.     The  bluestone  is  to  be  dissolved  in  water,  a  stock 

*  See  Bulletin  No.   144,  California  Experiment   Station. 


92  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT   STATION. 

solution  of  known  strength  being  most  convenient.  In  mixing  the  two, 
plenty  of  water  should  be  used  to  keep  them  well  diluted,  and  the 
mixture  well  churned  together,  strained,  and  diluted  with  the 
remainder  of  the  water. 

Relation  of  Spraying  and  Pruning.— The  early  time  of  spraying 
recommended  for  blight  control  is  apt  to  find  the  trees  unpruned  and 
with  considerable  foliage  still  on  the  branches.  This  at  first  seemed  a 
serious  obstacle  to  some,  but  experience  has  shown  that  even  in -this 
condition  the  trees  may  be  sprayed  with  perfect  success,  provided  a 
thorough  job  is  done.  It  is  very  desirable  to  have  the  trees  pruned 
before  spraying,  and  this  should  be  done  if  possible,  but  spraying 
should  on  no  account  be  delayed  beyond  the  proper  time  because  the 
trees  are  not  pruned.  If  the  pruning  can  not  be  clone  in  time  the 
spraying  should  proceed  very  thoroughly,  and  the  pruning  done  later. 

Application  of  the  Spray.— Instances  like  Nos.  32,  33,  61,  and  73, 
of  the  table,  show  the  results  of  poor  spraying.  Many  growers  went 
over  their  trees  a  second  time,  on  being  shown  their  mistakes.  The 
effort  should  be  made,  above  all,  to  cover  all  the  branches  and  fruiting 
twigs  completely  with  the  spray.  The  inexperienced  workman  soaks 
the  trunk  and  main  limbs,  but  leaves  untouched  much  of  the  small 
growth  which  bears  the  fruit  and  which  the  blight  particularly  affects. 
In  order  to  check  the  blight  infection  on  the  twigs,  those  twigs  must 
be  completely  covered  with  spray  before  infection  occurs.  The  least 
portion  of  a  twig  left  uncovered  is  as  exposed  to  infection  as  though 
there  wTas  no  spray  on  the  tree  at  all.  An  experienced  and  conscientious 
sprayer  goes  over  his  tree  systematically  and  completely,  leaving  no 
portion  uncovered  and  yet  wasting  no  material. 

E  elation  of  Peach  Varieties  to  Infection.— We  have  been  able  to 
find  no  fixed  rule  as  to  the  relation  of  the  different  peach  varieties  to 
the  blight.  In  some  sections  or  seasons  one  kind  has  been  much  the 
worst,  while  in  another  quite  a  different  condition  held  good.  No 
variety  has  been  at  all  immune  to  the  trouble,  but  all  quite  badly 
affected. 


Bulletin  191.  CALIFORNIA  PEACH  BLIGHT.  93 

THE  PEACH  BLIGHT  FUNGUS. 

The  fungus  causing  the  so-called  "blight,"  or  "shothole  fungus," 
has  been  identified  by  us  as  Coryneum  beyerinkii  Oud.  This  has  been 
mentioned  frequently  as  doing  damage  in  this  country,  though  never 
to  nearly  so  great  an  extent  as  in  California.  Trabut  reports  the  same 
fungus  as  occurring  extensively  in  Algeria  in  1904,  on  apricots, 
peaches,  and  cherries.4 

McAlpine,3  in  discussing  the  shothole  fungi  of  the  stone  fruit, 
describes  the  fungus  Clasterosporium  carpophilum  (Lev.)  Aderh., 
which  he  consideres  identical  with  Coryneum  beyerinkii.  Our  fungus 
appears  to  be  correctly  classified  as  Coryneum,  in  that  the  spores  are 
given  off  in  distinct  aggregations  from  a  special  stroma.  This  char- 
acteristic separates  it  definitely  from  Clasterosporium,  which  is  among 
the  Hyphomycetes.  Otherwise,  so  far  as  can  be  observed  from  descrip- 
tions and  plates,  the  Clasterosporium  of  McAlpine  is  identical  with  our 
Coryneum. 

So  far  as  mycological  characters  show,  there  is  only  one  species  of 
Coryneum  on  the  various  stone  fruits  in  California.  We  are  not  yet 
ready  to  report  upon  the  matter,  however,  from  the  standpoint  of 
cross-inoculation,  as  experiments  are  still  in  progress. 

The  mycelium  producing' the  spots  on  peach  leaves  and  shoots  during 
the  winter,  fruits  by  means  of  spore  pustules  which  occur  as  minute 
black  specks  (four  or  five)  near  the  center  of  the  more  or  less  circular 
spot.  The  tissue  of  the  leaves  so  affected  soon  drops  out,  so  that  it  is 
often  difficult  to  find  the  conidia  at  this  season  of  the  year,  especially 
where  only  the  young,  spotted  shoots  are  at  hand.  The  spots  on  the 
bark  are  more  often  sterile,  which  is  sometimes  true  of  the  leaf  spots 
as  well.  By  the  end  of  the  infection  period,  however,  the  spores  have 
become  quite  abundantly  scattered  about  on  the  twigs.  The  fertile 
spots,  on  sectioning,  show  distinct  pustules  with  well-developed  stro- 
mata,  which  push  out  until  the  epidermis  is  ruptured,  after  which  the 
short  conidiophores  with  their  olive-colored  elliptical  spores  appear  as 
dense  clusters  on  the  surface.     (Fig.  13.) 

Especially  on  twigs  from  which  the  affected  leaves  have  fallen  the 
eonidia  are  found  in  abundance  about  the  leaf  scars  and  roughened 
portions  of  the  bark  during  the  spring  and  summer.  (Fig.  14,  c.)  If 
a  late  rain  occurs  they  germinate,  causing  new  infection  on  the  remain- 
ing leaves,  and  are  ready  with  the  fall  rains  to  infect  and  kill  outright 
many  of  the  newly  formed  buds. 

1  Mich.  Agr.  Exp.  Sta.  Bull.  103,  p.  57.     1894. 

2  Ohio  Agr.  Exp.  Sta.  Bull.  92,  p.  225.     1898  and  other  State  Bulletins. 

3  Fungus  Diseases  of  the  Stone  Fruits  in  Australia  and  their  treatment,  bv 
D.  McAlpine.     March,  1902. 

4  Le  Coryneum,  Maladie  des  Arbres  a  Noyaux,  in  Bulletin  Agricole  de  l'Algerie 
et  de  la  Tunisie.     No.  10,  May,  1904.     By  Dr.  Trabut. 


94 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT    STATION. 


Though  many  of  the  eonidia  thus  distributed  are  those  which  fall 
from  the  spots  on  leaves  and  green  bark,  it  was  found  that  these  eonidia 


FIG.  13:    Longitudinal  section  through  a  Coryneum  pustule  on  peach  spot. 


Bulletin  191. 


CALIFORNIA   PEACH  BLIGHT. 


95 


reproduced  themselves  more  or  less  with  moisture  on  the  dead  outer 
cells  of  the  older  twigs.  This  occurs  often  as  a  mold-like  growth  on 
the  surface  of  the  bark,  much  as  in  artificial  media.  Characteristic 
pustules  are  found  on  the 
leaf  scars,  however,  some- 
times in  considerable  abun- 
dance. 

The  life  history  of  the 
Coryneum,  then,  as  shown 
by  our  experience,  is  as 
follows:  The  spores,  scat- 
tered profusely  over  the 
limbs,  germinate  as  soon  as 
enough  rain  has  fallen  to 
wet  them  up  thoroughly, 
usually  in  December  or 
January.  Spores  lying  on 
the  green  bark  of  new 
shoots  penetrate  the  tissue 
and  cause  the  characteristic 
spotting,  the  mycelium 
from  each  germinated  spore 
killing  a  small  area  of  the 
bark.  Spores  lying  about 
the  bud  scales  produce  a 
mycelium  which  penetrates 
and  kills  outright  both  the 
bud  and  quite  an  area  of 
surrounding  bark,  the  spot 
extending  from  one-fourth 
to  ,one  inch  in  length.  On 
the  spots  spore  pustules 
are  developed,  the  conidio- 
phores  being  produced  on 
a  stroma  under  the  epi- 
dermis which  is  ruptured 
by  the  spores.  (Fig.  13.)  When  the  buds  which  have  survived  the 
winter  attack  unfold  in  the  spring,  the  leaves  are  very  generally 
affected  by  the  fungus,  causing  small  dead  areas  in  the  leaf  tissue, 
which  soon  dry  up  and  fall  out,  causing  the  so-called  "shothole"  effect 
of  the  leaf.  Pustules  are  also  found  on  the  leaf  spots.  In  the  majority 
of  seasons  the  new  infection  ceases  at  the  end  of  April.  In  seasons 
where  a  late  rain  occurs  in  spring,  however,  the  spores  produced  on 


FIG.  14.  Coryneum  spores:  a,  from  petri  dish  colonies  in 
agar;  b,  from  prune  agar  tube  cultures;  c,  from  pus- 
tules on  peach  bark.    (All  drawn  to  same  scale.) 


96  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT   STATION. 

the  winter  infection  germinate  instead  of  remaining  dormant  till  fall 
or  winter,  and  not  only  leaves,  but  the  new  shoots  and  even  the 
young  fruit  become  spotted  at  this  time.  The  mycelium  in  the  newly 
affected  tissue  produces  spores  in  turn,  thus  furnishing  a  fresh  supply 
for  the  winter  attack. 

The  alarming  phase  of  the  fungus,  economically,  is  this  winter  kill- 
ing of  the  buds,  together  with  the  area  of  the  bark  about  the  bud  which 
is  involved  in  the  destruction.     As  new  growth  proceeds  the  tension 


FIG.  15.    Dried  petri  dish  culture  in  agar,  showing  colonies.    Natural  size. 

which  is  set  up  between  the  dead  and  the  growing  bark  surrounding  it 
causes  a  fissure,  from  which  the  gum  is  exuded.  This  gumming  from 
lesions  around  the  dead  buds  is  chiefly  confined  to  the  new  wood, 
since,  where  the  tree  has  sustained  the  attack  sufficiently,  old  wounds 
are  more  or  less  healed  over  at  the  time  of  the  next  year's  flow.  This 
attempt  at  healing  on  the  part  of  the  tree  causes  the  cankers  so  often 
found  on  the  Limbs  of  affected  trees.  Where  the  vitality  of  the  tree  is 
low,  however,  from  the  loss  of  buds,  leaves,  and  sap  for  perhaps  several 
consecutive  years,  there  are  sometimes  "gumming"  wounds  left  in  the 
older  wood. 


Bulletin  191. 


CALIFORNIA   PEACH   BLIGHT. 


As  yet  we  have  failed  to  procure  abundant  growth  in  culture  from 
spores  taken  from  the  bark  or  leaf.  This  is  to  be  accounted  for,  at 
least  in  part,  by  the  fact  that  the  copious  gum  exuded  from  the 
cankers  of  the  diseased  bark  produces  an  abundance  of  mold  spores 
of  various  kinds  besides  bacteria  and  yeasts,  which  outgrow  the  Cory- 
neum  in  initial  cultures.  Moreover,  during  the  winter  and  spring  the 
surface  of  the  tree  is  often  moist  and  sticky  throughout  from  escaping 
sap,  in  which  many  of  the  spores  have  already  germinated.  The  fact 
remains,  however,  that  mature  spores  under  seemingly  favorable  con- 
ditions in  whatever  season  usually  fail  to  grow  in  culture  when  taken 
from  the  tree. 
Often      only      one 


colony  is  secured 
out  of  a  dozen  or 
more  petri  dish 
cultures  in  peach 
or  ordinary  agar. 
Once  secured  in 
culture,  however,  it 
can  be  reproduced 
readily  in  either  of 
the  above  named 
media.  It  also 
grows  luxuriantly 
on  sterilized  peach 
twigs  in  tubes. 

The  colonies  in 
agar  petri  dish  cul- 
ture are  black,  with 
distinct  zones  of 
conidia,  the  col- 
onies being  submerged  in  the  medium.  (Fig. 
acid  agar  slants  the  fungus  produces  a  black 
posed  almost  entirely  of  spores.  The  mycelium, 
in  culture,  is  colorless.  On  sterile  twigs  distinct  pustules  are  formed, 
as  in  Fig.  16,  which  appear  to  the  naked  eye  as  black  specks  on  the 
epidermis.  The  size  of  the  pustule  is  more  or  less  uniform,  both  in 
natural  infection  and  in  twig  cultures,  measurements  varying  from 
100  m  to  166  pi  with  pustules  observed.  Shape  is  somewhat  cubical  or 
rounded.  The  spores  as  occurring  naturally  do  not  vary  materially  in 
length  from  those  in  agar  plates,  the  minimum  length  being  17  pi, 
maximum  44  yu,  average  30-40  pi.  Width  in  "  natural"  spores,  however, 
is  uniformly  about  13  yu,  $nd  number  of  cells  3  or  4,  rarely  5,  while  in 


FIG.  16.   Microphotograph  of  Coi 


pustule  on  sterilized  peach  twig. 

15.)  On  prune  or 
surface  crust  com- 
sparingly  produced 


98  UNIVERSITY    OP   CALIFORNIA EXPERIMENT    STATION. 

agar  colonies  width  is  about  6  //,  and  number  of  cells  from  3-12,  usually 
6  or  7.  On  sterile  twigs  the  spores  do  not  average  more  than  20  jjl  in 
length,  and  range  from  3  to  6  cells,  usually  4.     (See  Fig.  16.) 

The  peach  trouble  identified  as  being  caused  by  Helminthosporium 
carpophilum  (Lev.)  in  this  country  (see  cit.  1,  2,  3)  is  stated  by  Mc- 
Alpine  to  be  identical  with  his  Clasterosporium.  In  our  work  we  have 
found  the  spores  of  agar  cultures  particularly  suggestive  of  this  type, 
being  narrow,  of  uniform  width,  and  often  nearly  oblong  in  shape.  In 
short,  there  appear  to  be  two  types  of  spores  belonging  to  the  peach 
Cory iicum,  one  borne  on  a  distinct  stroma  in  pustules,  elliptical  and 
confined  to  three  or  four  cells,  the  others  of  hyphomycetous  origin, 
more  or  less  oblong,  and  from  3  to  12  cells.     (Fig.  14.) 

Vuillemin  in  1890  described  a  new  species  of  Ascospora  {A.  beyerinkii 
Yuill.)  which  he  considered  to  be  the  perfect  form  of  Coryneum 
beyerinkii.  Up  to  the  present  time  we  have  found  no  indication  of  an 
ascomycetous  stage  of  any  kind.  The  conidia  appear  to  live  over  the 
dry,  summer  season,  lodged  in  the  bud  scales  and  bark,  as  previously 
described.  That  it  is  possible  for  the  spores  to  live  several  months  in 
a  dry  condition  has  been  proved  by  laboratory  experiments. 

Of  the  various  molds  encountered  in  a  study  of  the  diseased  tissue, 
sooty  mold  and  a  species  of  Phyllosticta  have  been  found  most  con- 
stantly in  connection  with  it.  The  former  spreads  itself  over  the  sur- 
face of  the  dead  spots,  often  rather  soon  after  infection,  forming  a 
single  layer  of  connected  cells,  which  give  off  bud  conidia  in  the  manner 
characteristic  of  this  class  of  fungi.  The  Phyllosticta  is  found  more 
often  on  spots  which  are  thoroughly  dead  and  dry,  the  whole  surface 
being  dotted  with  the  small  pyenidia,  which  give  off  minute,  unicellular 
conidia  from  short  conidiophores.  The  writer  has  found  no  fungus 
associated  with  the  Coryneum  which  could  readily  be  confused  with  it 
as  the  cause  of  peach  blight. 


RECOMMENDATIONS  FOR  PEACH  BLIGHT  AND  CURL  LEAF  CONTROL. 

Spray  thoroughly  with  Bordeaux  mixture  between  November  1st 
and  December  15th.     The  work  may  begin  as  early  as  October  25th. 

Use  30  pounds  of  bluestone  and  35  pounds  of  quicklime  to  200  gal- 
loos  of  water.  If  materials  are  very  high,  somewhat  less  may  be  used, 
down  to  20-20-200. 

Prune  if  possible  before  spraying,  but  do  not  delay  the  work  on 
account  of  pruning. 

About  February  15th,  or  just  before  the  buds  open,  spray  again 
with   Bordeaux,  20-20-200,  or  lime,  salt  and  sulfur. 


STATION   PUBLICATIONS.  99 


STATION  PUBLICATIONS  AVAILABLE  FOR  DISTRIBUTION, 


REPORTS. 


1896.  Report    of    the    Viti cultural    Work    during    the    seasons    1887-93,    with    data 

regarding  the  Vintages  of  1894-95. 

1897.  Resistant    Vines,    their    Selection,    Adaptation,    and    Grafting.      Appendix    to 

Viticultural  Report  for  1896. 

1898.  Partial  Report  of  Work  of  Agricultural   Experiment   Station   for  the  years 

1895-96  and  1896-97. 
1900.     Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-1903. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-1904 

TECHNICAL   BULLETINS— ENTOMOLOGICAL  SERIES. 

Vol.  1,  No.  1 — Wing  Veins  of  Insects. 

No.  2 — Catalogue  of  the  Ephydridae. 

BULLETINS. 

Reprint.  Endurance  of  Drought  in  Soils  of  the  Arid  Region. 

No.  128.  Nature,  Value  and  Utilization  of  Alkali  Lands,  and  Tolerance  of  Alkali. 
(Revised  and  Reprint,  1905.) 

133.  Tolerance  of  Alkali  by  Various  Cultures. 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and  Supplement. 

141.  Deciduous  Fruits  at  Paso  Robles. 

142.  Grasshoppers  in  California. 

147.  Culture  Work  of  the  Substations. 

148.  Resistant  Vines  and  their  Hybrids. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

152.  Fumigation  Dosage. 

153.  Spraying  with  Distillates. 

154.  Sulfur  Sprays  for  Red  Spider. 
156.  Fowl  Cholera. 

158.  California  Olive  Oil ;  its  Manufacture. 

159.  Contribution  to  the  Study  of  Fermentation. 

160.  The  Hop  Aphis. 

161.  Tuberculosis  in  Fowls.      (Reprint.) 

162.  Commercial  Fertilizers.     (Dec.  1,  1904.) 

163.  Pear  Scab. 

164.  Poultry  Feeding  and  Proprietary  Foods.      (Reprint.) 

165.  Asparagus  and  Asparagus  Rust  in  California. 

166.  Spraying  for  Scale  Insects. 

167.  Manufacture  of  Dry  Wines  in  Hot  Countries. 

168.  Observations  on  Some  Vine  Diseases  in  Sonoma  County. 

169.  Tolerance  of  the  Sugar  Beet  for  Alkali. 

170.  Studies  in  Grasshopper  Control. 

171.  Commercial  Fertilizers.      (June  30,  1905.) 

172.  Further  Experience  in  Asparagus  Rust  Control. 

173.  Commercial  Fertilizers.     (December,  1905.) 

174.  A  New  Wine-Cooling  Machine. 

175.  Tomato  Diseases  in  California. 

176.  Sugar  Beets  in  the  San  Joaquin  Valley. 

177.  A  New  Method  of  Making  Dry  Red  Wine. 

178.  Mosquito  Control. 

179.  Commercial  Fertilizers.     (June,  1906.) 

180.  Resistant  Vineyards. 

181.  The  Selection  of  Seed-Wheat. 

182.  Analysis  of  Paris  Green  and  Lead  Arsenate.     Proposed  Insecticide  Law. 

183.  The  California  Tussock-moth. 

184.  Report  of  the  Plant  Pathologist  to  July  1,  1906. 

185.  Report  of  Progress  in  Cereal  Investigations. 

186.  The  Oidium  of  the  Vine. 

187.  Commercial  Fertilizers.      (January,   1907.) 

188.  Lining  of  Ditches  and  Reservoirs  to  Prevent  Seepage  and  Losses. 

189.  Commercial  Fertilizers.     (June,  1907.) 

190.  The  Brown  Rot  of  the  Lemon. 


1    • 


UNIVERSITY    OF   CALIFORNIA EXPERIMENT   STATION. 


CIRCULARS. 


No.  1. 

•i 

3. 
4. 
5. 
7. 
9. 
10. 

11. 
12. 
13. 
15. 

16. 
17. 

18. 
19. 
20. 
21. 


Texas   Fever. 

Blackleg. 

Hog  Cholera. 

Anthrax. 

Contagious  Abortion  in  Cows. 

Remedies  for  Insects. 

Asparagus  Rust. 

Reading  Course  in  Economic 

Entomology.      (Revision.) 
Fumigation  Practice. 
Silk   Culture. 

The   Culture   of   the    Sugar   Beet. 
Recent    Problems    in   Agriculture. 

What  a  University  Farm  is  For. 
Notes  on  Seed-Wheat. 
Why      Agriculture      Should      Be 

Taught  in   the   Public   Schools. 
Caterpillars  on  Oaks. 
Disinfection   of   Stables. 
Reading  Course  in  Irrigation. 
The  Advancement  of  Agricultural 

Education. 
Defecation    of    Must    for    White 

Wine. 


No.  23. 
24. 
25. 

26. 

27. 


28. 


29. 


30. 
31. 


32. 
33. 


Pure   Yeast   in   Wineries. 

Olive   Pickling. 

Suggestions  Regarding  Exam- 
ination of  Lands. 

Selection  and  Preparation  of 
Vine  Cuttings. 

Marly  Subsoils  and  the  Chlo- 
rosis or  Yellowing  of  Citrus 
Trees. 

A  Preliminary  Progress  Report 
of  Cereal  Investigations,  1905- 
1907. 

Preliminary  Announcement  con- 
cerning Instruction  in  Practi- 
cal Agriculture  upon  the 
University  Farm,  Davisville, 
Cal. 

White  Fly  in  California. 

The  Agricultural  College  and  Its 
Relationship  to  the  Scheme  of 
National    Education. 

White  Fly  Eradication. 

Packing  Prunes  in  Cans.  Cane 
Sugar   vs.    Beet   Sugar. 


Copies  may  le  had  on  application  to  Director  of  Experiment  Station,  Berkeley,  Cal. 


